US3619054A

US3619054A - Oil film imaging apparatus

Info

Publication number: US3619054A
Application number: US8134A
Authority: US
Inventors: William L Goffe
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1966-08-09
Filing date: 1970-01-16
Publication date: 1971-11-09
Anticipated expiration: 1988-11-09
Also published as: US3708287A

Abstract

An apparatus for forming an image, comprising a photoconductive insulating layer having a thin liquid film thereon and separated from an electrode by a small gap. After an electrical field has been established between the photoconductive layer and the electrode, the photoconductive layer is selectively illuminated causing liquid transfer in imagewise configuration onto the electrode. An image is also formed on the photoconductive insulating layer. Alternately, a thin liquid film is applied to both the photoconductive insulating layer and the electrode or solely to the electrode.

Description

United States Patent Inventor William L. Golle Webster. N.Y.

Appl. No. 8.134

Filed Jan. 16, 1970 Division of Ser. No. 571.343. Aug. 9. 1966 Patented Nov. 9, 1971 Assignee Xerox Corporation Rochester, N.Y.

OIL FILM IMAGING APPARATUS 6 Claims, 2 Drawing Figs.

US. Cl 355/16. 96/1 Int. Cl ..G03g15/14 Field ofSearch 35513.16.

Relerences Cited UNITED STATES PATENTS 2,904,431 9/1959 Yeates .1 355/17 X 2,975,052 3/1961 Fotland et a1 96/1 3,254,998 6/1966 Schwertz 355/11 X 3,317,316 5/1967 Bean et al.... 355/3X 3.383.993 5/1968 Yeh .1 355/3 Primary Examiner-Samuel S. Matthews Assislan! Examiner- Fred L. Braun Attorneys-James .l. Ralabate. Norman E. Schroder and Ronald Zibelli OIL FILM IMAGING APPARATUS This application is a divisional of application, Ser. No. 571,343 filed Aug.9, 1966.

This application relates to a novel means and method for image reproduction in which neither chemical reactions nor particulate materials are necessarily involved.

The invention will be described with relation to the drawing in which FIG. 1 is a schematic cross-sectional view of apparatus used in carrying out the invention, and FIG. 2 illustrates a method of precharging.

Two

platelike electrodes

10 and 12 are employed, each having at least one flat surface. The fiat surface of electrode 12 is covered with a thin layer, illustratively on the order of 0.002 inch thickness, of a photoconductive-insulating material 14. Such a material is one which is sufficiently resistive in darkness to be classified as a true electrical insulator but which becomes relatively more conductive upon exposure to radiation such as light. A vacuum-evaporated layer of vitreous selenium is the most common material of this classification and is a preferred material for use in the invention, but other materials with similar properties are known to the art and may be employed, and at lease one of these, a dispersion of zinc oxide in a resin binder, enjoys substantial commercial use. in one embodiment of the invention, electrode 10 is covered with a thin layer of insulating material on the order of a few microns in thickness. Either photoconductive insulating layer 14 or the facing surface of electrode 10 or both of them, in

that order of preference, is covered with a thin continuous layer of oil 16. The term oil as employed in this specification relates to any liquid material having a sufficiently low vapor pressure to form stable thin films and having an electrical resistivity sufficient to maintain potential gradients along the surface of the film. The films employed in the present invention are so thin that the resistivity required is met by most liquids but the vapor pressure requirement becomes more critical. Ester-type fluids sold for use as vacuum diffusion pump oils under such names as Octoil" (di-octal phthalate) made by Bendix Corporation Vacuum Division and Narcoil" (di-nonyl phthalate) made by National Research Corporation are particularly suitable for use in the invention. Oil film 16 must be very thin, preferably less than about 1 or 2 microns. Films of this thickness range can be recognized by the interference fringes which they produce.

A simple way to form the required oil film 16 is to separate

electrodes

10 and 12 and rub a dilute mixture of the selected oil in a volatile solvent, such as acetone, onto the surfaces with a piece of cotton wool. The resulting liquid film will be much thicker than desired but the solvent will rapidly evaporate and reduce the film thickness to the desired range.

After the oil film 16 has been formed,

electrodes

10 and 12 are positioned as illustrated. The gap 18 between electrode 10 and photoconductive insulating layer 14 should be on the order of 2 to 7 microns and preferably not more than about 0.001 inch. This spacing can be achieved in a practical manner by using thin spacers, not shown, between the electrodes l and 12 or between the electrode and the outer edge of photoconductive insulating layer l4. Strips of 0.00025 "Mylar" polyester film are effective spacers for use in the latter position. A DC power supply 20 and switch 21 is connected between

electrodes

10 and 12 and supplies a voltage in the range of 500-l,200 volts and generally about 600 volts in order to create an electric field in gap 18.

The only further step required to form an image is to selectively illuminate photoconductive-insulating layer 14 with an image pattern of light. To accomplish this, either electrode 10 or electrode 12 should be optically transparent. For this purpose, the electrodes may comprise sheets of transparent material with a thin transparent surface coating of an electrically conductive material. Glass coated with a thin transparent conductive layer of tin oxide is a preferred material and is available commercially under various trade names. The elec trodes may also be constructed by applying very thin metallic films or films of copper iodide to sheets of transparent material such as glass or plastics.

l have found that with the apparatus of FIG. 1 less exposure is required to satisfactorily illuminate photoconductive insulating layer 14 through electrode 12, and accordingly there is shown an original subject 22 illuminated by lamps 24 and which is focused by lens 26 through transparent electrode 12 onto the back of photoconductive insulating layer 14. Contact exposure may also be employed. However, I have also successfully carried out my invention by exposing layer 14 through a transparent electrode 10. When layer 14 is selectively illuminated, a visible image appears within a few seconds at most on each of photoconductive insulating layer 14 and electrode 10. The mechanism of image formation is not fully understood, but it appears that microscopic droplets of oil breakoff from the oil films and are transported across the gap 18 under the control of the pattern of resistivity in layer 14 as caused by the selective illumination from subject 22. if the oil films are thicker than indicated, large globules will transfer and fonn an image pattern of varying film thickness. lf gap 18 is thicker than indicated, there will be a loss in resolution. For similar reasons insulating layer ll, if used, should have a thickness in the order of microns.

lf layer 14 is illuminated through electrode 12, as shown, and electrode 10 is also transparent, then a visible image is immediately viewable by weak illumination through electrode 10 because photoconductive insulating layer 14 appears less sensitive to illumination through electrode 10 than through electrode l2. lf, however, a bright light is shown through electrode 12 or if subject 22 is replaced by a sheet of white paper, for example, the image will be erased and a new image can be formed later. When the original exposure conditions are restored the image will reappear. if the illumination is stopped or switch 21 is disconnected or

electrodes

10 and 12 are separated, a reasonable stable image will remain because extremely thin oil films such as I employ are not readily selfleveling. Once power supply 20 is disconnected or

electrodes

10 and 12 are separated, ambient illumination will have no effect on the images. The images are readily visible as an interference pattern and may be projected. Since the images are in the form of a thin liquid film they may be transferred by rolling to a sheet of paper or the like. The transferred image is not itself visible unless it has been treated with a first chemical which reacts with a second chemical in the paper to form a color reaction. Color reaction imaging per se is well known. The invisible transferred image can also be made visible by dusting the sheet with a finely divided powder which will selectively adhere to the areas having the greatest amount of oil. Such a development technique may also be employed to enhance the visibility of the oil image directly on electrode 10 or layer 14, but the dusted layer or electrode cannot be reused until the powder is washed off.

FIG. 2 illustrates a method of precharging photoconductive insulating layer 14. Layer 14 is passed beneath a coronagenerating device 30 which is maintained at a potential of several thousand volts relative to electrode 12 by a high-voltage DC power supply 32. if this operation is carried out in darkness, photoconductive insulating layer 14 can be charged to a high-surface potential, illustratively about 600 volts positive for selenium layers. The charging operation can be carried out after an oil film 16 has been formed on layer 14. After charging, the apparatus may be assembled in the manner shown in FIG. 1, except that power supply 20 can be of much lower voltage or even be replaced by a simple connecting wire. since the surface potential on layer 14 creates the necessary electric field in gap 18.

Using the apparatus of FIG. 1, the application of voltage from power supply 20 for a time as shown as one-half second or less is sufficient to form an image. If no insulating layer 1 1 is present, it appears that tiny droplets of oil are carried back and forth across gap 18 in illuminated areas, causing a redistribution of oil film 16 as originally laid down. It is postulated that there is an air breakdown occurring within the gap and that ion deposition on the oil film may locally destroy the surface tension and permit droplet formation in the presence of the electric field, which is strongest in illuminated areas. When the exposure intensity is increased to very high levels a reversal of image polarity is observed.

When an insulating layer 11, such as Staybelite" rosin ester, is employed on electrode 10, the apparatus is more sensitive to light and oil transport across the gap takes place in nonilluminated areas, instead of an illuminated areas when insulating film 11 is absent. It is believed that charge transfer takes place to the insulating layer in areas of exposure and that the potential built up on insulating layer 1 1 reduces the field in the gap and prevents transport of oil across the gap. 1f the apparatus of FIG. 1 is tested without oil film 16 but with insulating film 11 an electrostatic charge pattern is observable on insulator ll after the electrodes have been separated. By using the apparatus of FIG. 1 in connection with an insulating film 11, comprising a few microns of Staybelite," image resolutions of 47 lines as per millimeter have been achieved with storage life times in excess of a minute. For maximum resolution, all film and gap thicknesses should be kept as small as possible. Under optimum conditions the amount of oil transferred across the gap is very small, but is sufficient to form a visible interference pattern or for use in the other previously described ways.

While the present invention has been particularly described in terms of a specific embodiment thereof, it will be understood that in view of the foregoing specification numerous deviations therefrom and modifications thereupon may be readily devised by those skilled in the art without departing from the present teaching. Accordingly, the present invention is to be broadly construed and limited only by the scope and spirit of the claims now appended hereto.

What is claimed is:

l. Image-forming apparatus comprising:

a photoconductive-insulating layer supported on a first electrode;

a second electrode positioned substantially parallel to said photoconductive-insulating layer and defining a gap of less than 0.00l inch therefrom;

a nongap-bridging nonvolatile-insulating liquid interference film positioned on at least one of said photoconductiveinsulating layer and said second electrode;

DC power supply means connected between said first and second electrodes; and

means to project an optical image on said photoconductiveinsulating layer, whereby an image pattern of said liquid is formed on said second electrode and said photoconductive-insulating layer.

2. The apparatus of claim 1 in which said first electrode is transparent and said optical image is projected through said first electrode onto said photoconductive-insulating layer.

3. The apparatus of claim 2 in which said second electrode is covered with a thin layer of insulating material.

4. The apparatus of claim 1 in which said second electrode is covered with a thin layer of insulating material.

5. The apparatus of claim 1 in which said second electrode is transparent and said optical image is projected through said second electrode and said gap onto said photoconductive insulating layer.

6. The apparatus of claim 5 in which said second electrode is covered with a thin layer of insulating material.

i I i t

Claims

2. The apparatus of claim 1 in which said first electrode is transparent and said optical image is projected through said first electrode onto said photoconductive-insulating layer.
3. The apparatus of claim 2 in which said second electrode is covered with a thin layer of insulating material.
4. The apparatus of claim 1 in which said second electrode is covered with a thin layer of insulating material.
5. The apparatus of claim 1 in which said second electrode is transparent and said optical image is projected through said second electrode and said gap onto said photoconductive insulating layer.
6. The apparatus of claim 5 in which said second electrode is covered with a thin layer of insulating material.